Question

I want to add functionality to javascript-mode so that, whenever I save a Javascript file on the current buffer, it creates a minified file of it in a directory defined with relative path such as ../foo with the same file name. How can I do that?

I am using Ubuntu as OS. Is there a good program that I should call in emacs for doing this?

Answer 1

You can add a function to the after-save-hook, but make it specific to javascript mode, add the hook in the js-mode-hook. Also, set add-hook‘s fourth parameter LOCAL to a non-nil value. For example:

(add-hook 'js-mode-hook
          (lambda () 
            (add-hook 'after-save-hook 'my-minify-function nil t)))

(defun my-minify-function ()
  (shell-command (format "minify %s ../foo/%s" 
                         (buffer-file-name) 
                         (buffer-file-name))))